As different proteins have different compositions of amino acids, different protein molecules precipitate at different concentrations of salt solution.
Unwanted proteins can be removed from a protein solution mixture by salting out as long as the solubility of the protein in various concentrations of salt solution is known. After removing the precipitate by filtration or centrifugation, the desired protein can be precipitated by altering the salt concentration to the level at which the desired protein becomes insoluble.

Fractionation
. Fractionation makes it possible to isolate groups
of proteins, or fractions from total proteome
Simplifies analysis of complex protein mixtures
. Allows for improved resolution when an individual
fraction is analyzed
Provides less crowded 2-D maps

alting Out precipitation
Most proteins are less soluble at high salt concentrations, an
effect called salting out.
Salting In
Proteins are usually poorly soluble in pure water. Their
solubility increases as the ionic strength increases, because
more and more of the well-hydrated inorganic ions are bound
to the protein's surface, preventing aggregation of the
molecules (salting in).

-DIALYSIS BAG
C CUT OFF SIZE
BuFFER
( 1 NTER EST

Questions the curious you

Protein purification refers to the
a) Purification of proteins
b) Separation of proteins from other biomolecules
c) Separation of a particular protein from other contaminating proteins
d) all of these

Protein separation techniques are often based on the following properties except
a) solubility of the protein
b) viscosity of the protein
c) charge of protein
d) specific binding affinity of the protein

Which of the following detergent is commonly used to release integral proteins from its
membranes?
a) urea
b) dimethyl sulphoxide
c) triton X 100
d) cyanogen bromide